This is one that always baffled me: it's a very simple intelligence routine
to take a string fragment and:
1) check for www.<whatever>.{edu|org|com|net|.com.uk|.com.au}
2) check for <whatever>.{edu|org|com|net|.com.uk|.com.au}
3) check for urls in the user's history list that have <whatever>
4) soundex searching of #3

For IE3:

> An AutoSearch feature, which was added at the last moment,> lets users run Yahoo searches directly from the URL> address field by typing "go" "find" or "?" and the search> term. We found this only slightly more useful than going> to a search site ourselves, and we were disappointed that> we could not go to a site by simply typing the middle of> the URL.>> For example, if we typed "Boston" in the address field,> we received an error. If we typed "go Boston" we went to> a Yahoo search page that showed us every entry related> to Boston. In Navigator, typing "Boston" brought us to> www.boston.com.